Tuberculosis Flashcards
What are the main species of bacteria causing tuberculosis?
Mycobacterium tuberculosis
Mycobacterium bovic
Mycobacterium leprae = leprosy
Features of tuberculosis bacteriae?
Non motile bacillus Slow growing Aerobic Very thick cell wall Resistant to acid, alkai Resistant to neutrophils, macrophages
How is TB transmitted?
Person with TB coughs/sneezes
Respiratory droplets evaporate, mycobacteria remains airborne
Eliminated by UV outside
Larger droplets impact on large airways and are cleared, smaller droplets <5microM slowly proliferate
Bovis from cow’s milk, deposited in cervical/intestinal lymph nodes
What is the immunopathology of TB granulomas?
Activated macrophages become epitheliod cells, which then fuse to form Langhan’s giant cells. This forms a granuloma.
In TB, there is central caseating necrosis.
Th1 cell mediated immunological response. Eliminates invading mycobacteria, but destroys tissue.
Pathology of TB
Usually children
80% focus in alveolus
Mycobacteria spreads via lymphatics to draining hilar lymph nodes.
Seeding of mycobacteria to all organs
Symptoms/Signs at beginning of TB infection?
Usually no symptoms of primary infection.
Erythema nodosum
Possible fever/malaise
In a small number (1%), primary infection progresses.
Primary focus continues to enlarge, leading to cavitation.
Enlarged hilar lymph compresses bronchi leading to lobar collapse
Enlarged lymph node discharges into bronchus, leading to TB bronchopneumonia
What can cause post-primary disease in TB?
Reactivation of mycobacterium from latent primary infection disseminated by the blood stream around the body.
New re-infection from outside source, in a susceptible previous infected host.
- this leads to a different host response because of previous sensitisation
What are some further problems in post-primary TB?
Pulmonary disease Lymph node enlargement Infection of bones/joints Genitourinary infection Infertility Constrictive pericarditis Ascites Addison's Lupus
Symptoms/Signs of established TB?
May be none for many months
Progressive over several months
General respiratory symptoms Cough Sputum Haemoptysis Pleuritic pain SOB Malaise Fever Weight loss Night sweats
Crackles
Bronchial breathing
Finger clubbing rare unless very chronic
Risk factors for TB and typical histories?
PMH of diabetes, immunosuppressive diseases, previous TB Immunosuppressant drugs Alcohol use IVDA Poor social circumstances Immigrants from high incidence areas Often no signs
How do you diagnose TB in terms of investigations?
3 sputum specimens on successive days.
- ZN stain
- Sputum culture (can take 8 weeks)
- Sputum PCR
CXR
- patchy shadowing, often in apices, or apex of lower lobes
- often bilateral
If sputum negative?
- CT thorax
- Bronchoscopy
- Biopsy and ZN stain, culture etc.
- Pleural aspiration and biopsy
What is the treatment for TB?
Rifampicin and Isoniazid for 6 months
Ethambutol, Pyrazinamine for 2 months
(4 for 2, then 2 for 4)
Legal requirement to notify all cases, and specialist treatment only.
Think HIV
Examples of side effects of TB treatments?
Rifampicin
- orange urine/teras
- induces liver enzymes, prednisolone, anticonvulsants
- renders oral contraceptive inert
- hepatitis
Isoniazid
- hepatitis
- peripheral neuropathy
Ethambutol
- optic neuropathy
Pyrazinamine
- gout
What is contact tracing in TB and how is it done?
Identify source and transmission of TB
In general
- first screen close household contacts
- if close contacts infected then organism is virulent and has high transmission
- screen casual contacts also
How is screening for TB done?
If <16 and no BCG, should have no immunity to tuberculoprotein
- do tuberculin test (heaf/mantoux)
If positive and CXR normal, then give prophylaxis
If positive and CXR abnormal, then it’s TB
Repeat screening after 6 weeks
If has BCG, do CXR
- normal = do nothing
- abnormal? do investigations and treat
